Gold plating



United States Patent 3,092,559 GOLD PLATING Donald Gardner Foulke,Watchung, and Edwin Cornell Rmker, Morristown, N..i., assiguors toSel-Rex Corpoi-anon, Nutley, N.J., a corporation of New Jersey NoDrawing. Filed May 1, 1961, Ser. No. 106,541 9 Claims. (Cl. 204-43) Thisinvention relates to gold plating and more particularly to thedeposition of bright, relatively low-carat deposits.

Although there are a number of processes for the deposition of bright24-carat gold and near-24-carat gold deposits, processes are notavailable for the deposition of bright lower carat electroplates. Theobvious advantage of a low-carat deposit is the reduced cost of thedeposit per unit of thickness, with the electroplate still retaining thecorrosion and tarnish resistance of gold alloys as well as the color toa considerable extent.

One method for providing bright gold deposits was described by Rinker(US. Reissue No. 24,582). However, when the amount of silver in thedeposit exceeds about two percent the deposits become greenish in colorand are lacking in attractiveness.

Among the objects of this invention is to provide a composition andprocess for obtaining bright deposits of about 14 to about 23.5 caratgold with improved color.

This invention is based on the discovery that the addi tion of a smallamount of an alkali soluble titanium compound to an alkali cyanide goldplating bath containing silver not only leads to an extended brightrange and more brilliant deposits, but the addition of this additionagent also leads to deposits less green in color than those obtainedfrom baths containing larger quantities of silver than as describedunder said US. Reissue Patent No. 24,582. Exceptionally brilliantgold-silver alloy deposits are obtained when the titanium compound isadded in conjunction with a small amount of an alkali-soluble seleniumcompound.

This invention is carried out most advantageously by employing a typicalcyanide gold plating solution containing 4-32 g./l. of gold, 10 to 200grams per liter of alkali cyanide, and 0.1 to 12 g./l. of potassiumsilver cyanide. The prefer-red composition and limiting concentrationsare shown in Table 1 (below) from which it is obvious that a wide rangefor each constituent is possible. Obviously, the ratio of silver to goldin the deposit will vary considerably dependent upon the AuzAg ratio inthe bath, but wide variations can be accomplished by manipulation of thebrightener content due to varying effects upon the polarization curvesfor gold and silver. Most striking is the development of low caratdeposits going from gold to white with little evidence of the greencolor common to low-carat, gold-silver alloys.

Any titanium compound soluble in the bath may be employed, butparticularly satisfactory results have been obtained by adding titaniumcoordination compounds having at least one ligand selected from theclass consisting of polyols and alkanolamines, since these compounds areunusually stable for titanium salts in aqueous solution. Theaminoalcohol titanates which may be employed in the practice of thepresent invention include the titanate esters of aminoalcohols whichhave the formula,

wherein R is selected from the group consisting of ethylone and alkylsubstituted ethylene radicals and R and R" are selected from the groupconsisting of hydrogen, alkyl hydrocarbon groups, B-amino-alkyl andB-hydroxy alkyl "ice radicals. These aminoa-lcohol esters are stabilizedin solution by the addition to said ester of a compound selected fromthe group consisting of inositol, sucrose and the more or less relatedsaturated and/ or unsaturated straight chain aliphatic alcohols andmonocarboxylic acid derivatives thereof containing 3 to 7 carbon atomsand 3 to 6 hydroxy groups such as gluconic, sorbic, aconitic,glucoheptonie acids and the alkali salts thereof. The mechanism of thestabilization may involve the formation of a coordination compoundbetween the aminoalcohol titanates and the polyhydroxy compounds. Theexact structure is not known, but in general the greater the number ofhydroxy groups, the more efilective is the compound as a stabilizer.

Aminoalcohol titanates, per se, are disclosed in US. Patent No.2,894,966 but the following Examples A-C illustrate specific methods ofproducing such titanium compounds.

EXAMPLE A A suitable stabilized ethanolamine titanate may be prepared byadding 1 mole of ethanolamine to mole of isopropyl titanate. Thesolution will become warm, then mole of sorbitol hemihydrate in 100 ml.of water is added and the mixture is heated to drive oil. the isopropylalcohol after which the stabilized ethanolamine titanate is taken up in250 ml. of water. The aqueous solution serves as the addition agent forthe gold bath.

EXAMPLE B The triethanolamine titanate was prepared by the same processas set forth in Example A by substituting 1 mol of triethanolamine forthe ethanolamine.

EXAMPLE C The solution of titanates of Examples A or B may also bestabilized by substituting or" a mol of inositol, sodium gluconate,sodium glucoheptonate, or similar polyliydroxy compound for thesorbit-ol.

The gold bath normally is made up with potassium salts according toTable I, but sodium salts may be substituted in which case somewhat lessbrilliancy may be expected.

When the selenium compound is added a minimum of about .03 g./l. isrequired to enhance the result noticeably.

The following specific examples of the gold plating bath compositionsyielding bright deposits support the ranges given in Table I.

EXAMPLE 1 A bath containing 4 g./l. of gold as KAu(CN) 0.04 g./l. ofsilver as KAg(CN) 0.05 g./l. of titanium as stabilized triethanolaminetitanate and 10 g./l. of free potassium cyanide gave bright, yellowishgold deposits on a 2.5 x 10 cm. brass panel plated at .2 ampere/dmP'.

EXAMPLE 2 A gold plating solution containing 8 g./l. of gold (aspotassium gold cyanide), 3 g./l. of silver (as potassium silvercyanide), g./l. of potassium cyanide, 0.1 g./l. of titanium (as theethanolamine titanate of Example A) and 0.1 g./l. of seleniumdiethyldithio-carbamate. De-

posits were obtained on 2.5 x 10 cm. panels which were bright at 0.4,0.6, 1.2, and 1.8 amperes/dmF.

EXAMPLE 3 A bath was made up containing 8 g./l. of gold added aspotassium gold cyanide, 4 gl/l. of silver, added as potassium silvercyanide, 90 g./l. of potassium cyanide and carbon-treated with 1g./lite-r of carbon. At 0.6, 0.8 and 1.2 amperes/dm. the deposit washazy. The 0.1 g./'l. of titanium as triethanolamine titanate of ExampleB and 0.1 g./l. of selenium as sodium selenite was added. The depositbecame brilliant at 0.6, 0.8 and 1.2 amperes/dmf EXAMPLE 4 A bath wasmade up containing 8 g./l. of gold, added as potassium gold cyanide, 4g/l. of silver, added as potassium silver cyanide and 90 g./l. ofpotassium cyanide. As in Example 3 the deposits were hazy at 0.6, 0.8and 1.2 amperes/dmf". The addition of 0.1 g./l. of titanium asstabilized triethanolamine titanate eliminated the hazy condition at 0.6and 0.8 amperc/dmF.

EXAMPLE 5 A gold plating solution was prepared as for Examples 2 and 3.A characteristic haxy golden deposit was brightened considerably by aslittle as 0.05 g./l. of stabilized triethanolamine titanate and becamebrilliant when 0.1 g./l. of selenium diethyldithi-o-carbamate was alsoadded.

EXAMPLE 6 A bath was made up containing 32 g./l. of gold as KAu(CN) =12g./ l. of silver added as KAg(CN) 90 g./l. of potassium cyanide alongwith 0.1 g./l. of titanium as stabilized triethanolamine titanate and0.025 g./l. of selenium as metallic selenium was added to the bath.Bright, white gold deposits were obtained at 4, 6, 8 and 10amperes/dmfi. At 20 amperes/clrn. the deposit was slightly hazy.

The features and principles underlying the invention described above inconnection with specific exemplifica- 'tions will suggest to thoseskilled in the art many other modifications thereof. It is accordinglydesired that the appended claims shall not be limited to any specificfeature or details thereof.

We claim:

1. An aqueous alkali cyanide gold plating bath containing about 4 to 32g./l. of gold, about 0.04 to 12 g./l. of silver, about 10 to 200 g./l.of alkali cyanide and about 0.05 to 5 g./l. of a water-soluble titaniumcompound.

2. The gold plating bath of claim 1 in which the titanium compound is anaminoalcohol titanate.

3. The gold plating bath of claim 2 in which the aminoalcohol titanateis stabilized by the addition of polyaleohol compound.

4. An aqueous alkali cyanide gold plating bath containing about 4 to 32g./-l. of gold, about 0.04 to 12 g./l. of silver, about 10 to 200 g./l.of alkali cyanide, about 0.05 to 5 g./l. of stabilized amin'oalooholtitanium compound and about 0:03 to 3 g./l. of a bath-soluble seleniumcompound.

5. An aqueous cyanide gold plating bath according to claim 4 wherein thebath-soluble titanium compound is a stabilized triethanolamine titanateand the gold and silver are present as potassium gold cyanide andpotassium silver cyanide, respectively.

6. A process of producing a bright gold alloy which compriseselectrodepositing a gold-silver alloy of about 23.5 to about 14-ca1'atfrom an aqueous solution containing from about 4 to 32 g./l. of goldadded as alkali gold cyanide, about 0.4 to 12. g./l. of silver added asalkali silver cyanide, about 10 10,200 g./l. of free alkali cyanide andabout 0.05 to 5 g./l. of a soluble titanium compound.

7. A process as claimed in claim 6 wherein the soluble titanium compoundis an alcoholamine titanate.

8. A process according to claim 6 comprising adding to said bath, inaddition, 0.03 to 3 g./l. of selenium.

9. A process according to claim 8 wherein the titanium compound ist-riethanolamine titanate and the selenium compound isdiethyldithio-carbamate.

References Cited in the file of this patent UNITED STATES PATENTS Re.24,582 Rinker Dec. 23, 1958' 1,731,212 Davignon Oct. 8, 1929

1. AN AQUEOUS ALKALI CYANIDE GOLD PLATING BATH CONTAINING ABOUT 4 TO 32G./L. OF GOLD, ABOUT 0.04 TO 12 G./L. OF SILVER, ABOUT 10 TO 200 G./L.OF ALKALI CYANIDE AND ABOUT 0.05 TO 5 G./L. OF A WATER-SOLUBLE TITANIUMCOMPOUND.